An ultrasound or acoustic angioplasty catheter as described in U.S. Pat. No. 5,423,797, issued Jun. 13. 1995 in the name of Adrian et al., reduces transmission losses, and reduces unwanted heating of the transmission member, by adapting the catheter to be driven by a rotary motor, and by generating the acoustic energy within the body, rather than, as in the prior art, generating the acoustic energy without or outside the body and coupling it into the body by means of a transmission member such as a longitudinally excited wire. The catheter as described therein includes an elongated body defining a distal end and a proximal end, and a shaft extending longitudinally through the body. The shaft includes a drive coupling arrangement near the proximal end of the catheter, which is adapted to be coupled to the rotary motor, for causing the shaft to be driven in a continuous-rotation manner. A rotary-to-axial motion converter is coupled to the shaft near the distal end of the catheter, for converting the rotary motion into axial motion in the form of acoustic energy. In a particularly advantageous embodiment, the rotary-to-axial motion converter includes a swash plate coupled to the shaft for being rotationally driven thereby. The swash plate defines a surface which, at a reference point which is angularly fixed relative to the catheter body, moves axially in response to the rotary motion of the swash plate. In another embodiment, the follower engages a sinusoidal groove in the periphery of the drive coupling arrangement.
Another acoustic arrangement is described in U.S. Pat. No. 5,569,179, issued Oct. 29, 1996 in the name of Adrian, in which the catheter includes an elongated shaft defining a distal end and a proximal end. The proximal end of the shaft includes a coupling arrangement for coupling to a rotary drive such as an external rotary motor. The catheter also includes a rotary-to-axial motion converter coupled to the distal end of the shaft. The motion converter includes at least a first magnetic pole mechanically coupled to the distal end of the shaft for being rotated thereby along an arc. The motion converter also includes a nonrotating reciprocating device or follower, and at least a second magnetic pole which is located so as to come within the magnetic influence of the first magnetic pole during each the rotation of the shaft. During each rotation, the two magnetic poles attract or repel, for causing reciprocating axial motion of the reciprocating device relative to the distal end of the shaft. This motion generates acoustic energy in the fluid medium located at the distal end of the catheter. An advantage of some of the embodiments over some of the swash-plate embodiments of the prior art is that a spring arrangement is not needed to return the follower after an excursion in one direction, which reduces heating losses in the spring.
Yet another acoustic catheter arrangement having a low-friction drive is described in U.S. Pat. No. 5,593,415, issued Jan. 14, 1997 in the name of Adrian., in which the rotary-to-axial motion converter includes a rotary portion coupled to the shaft for being driven in a rotary manner thereby, and the rotary portion of the rotary-to-axial motion converter defines a bearing surface which includes portions which, relative to a point fixed on the body of the catheter, move axially in response to rotation of the rotary portion. The axial motion reciprocates in response to the rotation of the shaft. The catheter also includes a magnetic arrangement coupled to the rotary portion of the rotary-to-axial motion converter and to the follower, for generating a magnetic force between the bearing surface of the rotary portion of the rotary-to-axial motion converter and the bearing surface of the follower, which force tends to reduce friction between the bearing surfaces of the rotary portion and the follower portion of the rotary-to-axial motion converter.
An easily fabricated rotary acoustic ablation catheter is described in U.S. patent application Ser. No. 08/829,052, filed Mar. 31, 1997 in the name of Adrian, in which the rotary-to-axial motion converter of the catheter further comprises a rotary driver coupled to the shaft, for being driven in a rotary manner thereby in response to rotation of the shaft. The rotary driver includes a cylindrical shell with an outer surface having the general outer shape of a right circular cylinder defining distal and proximal ends. The cylindrical shell also defines an inner surface with a guide path which is circumferentially continuous about the circumference of the inner surface of the shell. The guide path has portions which lie closer to the distal end of the cylindrical shell and other portions which lie closer to the proximal end of the shell. The rotary-to-axial motion converter of the catheter also includes a follower coupled to the guide path. The follower is fixed against rotation, so it cannot rotate with the rotary driver. The follower is mechanically coupled to the guide path, for being reciprocally driven in an axial manner in response to rotation of the shaft, shell, and guide path. This arrangement has the advantage of minimizing the diameter of the rotary-to-axial-motion converter.
Improved rotationally driven acoustic ablation catheters are desired.